The present invention relates to an ignition apparatus is suitable for use with a gas turbine engine.
Existing solid state ignition designs have difficulty in achieving high levels of output current (over 1,500 amps) at high temperatures (over 125.degree. C.) due to both static (leakage current) and dynamic (switching) losses in the solid state switch.
U.S. Pat. No. 3,505,563 discloses an ignition apparatus having a storage capacitor which stores charge for creating and maintaining a discharge through an igniter plug. The capacitor is connected via a spark gap to the igniter plug. The spark gap has a voltage rating such that the voltage across the capacitor when fully charged is insufficient to break down the spark gap.
The spark gap has a trigger terminal which is connected to a voltage pulse producing circuit. This circuit comprises a transformer whose secondary is connected to the trigger electrode of the spark gap. A capacitor is periodically discharged by a thyristor into the primary winding of the transformer. The output pulse produced by the secondary winding of the transformer is sufficient to initiate breakdown of the spark gap so as to control discharge of the capacitor through the igniter plug.
Such an arrangement requires the use of a spark gap having a separate trigger terminal. Thus, although the stress on the thyristor is reduced by employing a voltage step-up transformer, this arrangement is more complicated and expensive. Further, the capacitor is still required to be charged to a voltage sufficient to initiate discharge in the igniter plug.